Flexible Circuit Electrode Array

ABSTRACT

A flexible circuit electrode array with more than one layer of metal traces comprising: a polymer base layer; more than one layer of metal traces, separated by polymer layers, deposited on said polymer base layer, including electrodes suitable to stimulate neural tissue; and a polymer top layer deposited on said polymer base layer and said metal traces. Polymer materials are useful as electrode array bodies for neural stimulation. They are particularly useful for retinal stimulation to create artificial vision, cochlear stimulation to create artificial hearing, or cortical stimulation many purposes. The pressure applied against the retina, or other neural tissue, by an electrode array is critical. Too little pressure causes increased electrical resistance, along with electric field dispersion. Too much pressure may block blood flow.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a divisional application of U.S. patent applicationSer. No. 11/934,627, filed Nov. 2, 2007, which claims the benefit ofU.S. Provisional Application No. 60/856,455, “Flexible Circuit ElectrodeArray”, filed Nov. 2, 2006 and is a Continuation-In-Part of U.S.application Ser. No. 11/821,328, “Flexible Circuit Electrode Array withAt Least One Track Opening,” published as US 2007/0265665 on Nov. 15,2007, which claims the benefit of U.S. Provisional Application No.60/815,311, filed Jun. 21, 2006, “Flexible Circuit Electrode Array withat Least One Tack Opening.”

U.S. application Ser. No. 11/821,328 is a Continuation-In-Part of U.S.application Ser. No. 11/413,689, filed Apr. 28, 2006, “Flexible CircuitElectrode Array,” published as US 2006/0259112 on Nov. 16, 2006, whichis a Continuation-In-Part of U.S. application Ser. No. 11/207,644, filedAug. 19, 2005, “Flexible Circuit Electrode Array,” published as US2006/0247754 on Nov. 2, 2006, which claims the benefit of U.S.Provisional Application No. 60/676,008, filed Apr. 28, 2005, “Thin FilmElectrode Array”, all of which are incorporated herein by reference.

GOVERNMENT RIGHTS NOTICE

This invention was made with government support under grant No.R24EY12893-01, awarded by the National Institutes of Health. Thegovernment has certain rights in the invention.

FIELD OF THE INVENTION

The present invention is generally directed to neural stimulation andmore specifically to an improved electrode array for neural stimulation.

BACKGROUND OF THE INVENTION

In 1755 LeRoy passed the discharge of a Leyden jar through the orbit ofa man who was blind from cataract and the patient saw “flames passingrapidly downwards.” Ever since, there has been a fascination withelectrically elicited visual perception. The general concept ofelectrical stimulation of retinal cells to produce these flashes oflight or phosphenes has been known for quite some time. Based on thesegeneral principles, some early attempts at devising prostheses foraiding the visually impaired have included attaching electrodes to thehead or eyelids of patients. While some of these early attempts met withsome limited success, these early prosthetic devices were large, bulkyand could not produce adequate simulated vision to truly aid thevisually impaired.

In the early 1930's, Foerster investigated the effect of electricallystimulating the exposed occipital pole of one cerebral hemisphere. Hefound that, when a point at the extreme occipital pole was stimulated,the patient perceived a small spot of light directly in front andmotionless (a phosphene). Subsequently, Brindley and Lewin (1968)thoroughly studied electrical stimulation of the human occipital(visual) cortex. By varying the stimulation parameters, theseinvestigators described in detail the location of the phosphenesproduced relative to the specific region of the occipital cortexstimulated. These experiments demonstrated: (1) the consistent shape andposition of phosphenes; (2) that increased stimulation pulse durationmade phosphenes brighter; and (3) that there was no detectableinteraction between neighboring electrodes which were as close as 2.4 mmapart.

As intraocular surgical techniques have advanced, it has become possibleto apply stimulation on small groups and even on individual retinalcells to generate focused phosphenes through devices implanted withinthe eye itself. This has sparked renewed interest in developing methodsand apparati to aid the visually impaired. Specifically, great efforthas been expended in the area of intraocular retinal prosthesis devicesin an effort to restore vision in cases where blindness is caused byphotoreceptor degenerative retinal diseases; such as retinitispigmentosa and age related macular degeneration which affect millions ofpeople worldwide.

Neural tissue can be artificially stimulated and activated by prostheticdevices that pass pulses of electrical current through electrodes onsuch a device. The passage of current causes changes in electricalpotentials across visual neuronal membranes, which can initiate visualneuron action potentials, which are the means of information transfer inthe nervous system.

Based on this mechanism, it is possible to input information into thenervous system by coding the sensory information as a sequence ofelectrical pulses which are relayed to the nervous system via theprosthetic device. In this way, it is possible to provide artificialsensations including vision.

One typical application of neural tissue stimulation is in therehabilitation of the blind. Some forms of blindness involve selectiveloss of the light sensitive transducers of the retina. Other retinalneurons remain viable, however, and may be activated in the mannerdescribed above by placement of a prosthetic electrode device on theinner (toward the vitreous) retinal surface (epiretinal). This placementmust be mechanically stable, minimize the distance between the deviceelectrodes and the visual neurons, control the electronic fielddistribution and avoid undue compression of the visual neurons.

In 1986, Bullara (U.S. Pat. No. 4,573,481) patented an electrodeassembly for surgical implantation on a nerve. The matrix was siliconewith embedded iridium electrodes. The assembly fit around a nerve tostimulate it.

Dawson and Radtke stimulated cat's retina by direct electricalstimulation of the retinal ganglion cell layer. These experimentersplaced nine and then fourteen electrodes upon the inner retinal layer(i.e., primarily the ganglion cell layer) of two cats. Their experimentssuggested that electrical stimulation of the retina with 30 to 100 μAcurrent resulted in visual cortical responses. These experiments werecarried out with needle-shaped electrodes that penetrated the surface ofthe retina (see also U.S. Pat. No. 4,628,933 to Michelson).

The Michelson '933 apparatus includes an array of photosensitive deviceson its surface that are connected to a plurality of electrodespositioned on the opposite surface of the device to stimulate theretina. These electrodes are disposed to form an array similar to a “bedof nails” having conductors which impinge directly on the retina tostimulate the retinal cells. U.S. Pat. No. 4,837,049 to Byers describesspike electrodes for neural stimulation. Each spike electrode piercesneural tissue for better electrical contact. U.S. Pat. No. 5,215,088 toNorman describes an array of spike electrodes for cortical stimulation.Each spike pierces cortical tissue for better electrical contact.

The art of implanting an intraocular prosthetic device to electricallystimulate the retina was advanced with the introduction of retinal tacksin retinal surgery. De Juan, et al. at Duke University Eye Centerinserted retinal tacks into retinas in an effort to reattach retinasthat had detached from the underlying choroid, which is the source ofblood supply for the outer retina and thus the photoreceptors. See,e.g., E. de Juan, et al., 99 μm. J. Ophthalmol. 272 (1985). Theseretinal tacks have proved to be biocompatible and remain embedded in theretina, and choroid/sclera, effectively pinning the retina against thechoroid and the posterior aspects of the globe. Retinal tacks are oneway to attach a retinal electrode array to the retina. U.S. Pat. No.5,109,844 to de Juan describes a flat electrode array placed against theretina for visual stimulation. U.S. Pat. No. 5,935,155 to Humayundescribes a retinal prosthesis for use with the flat retinal arraydescribed in de Juan.

SUMMARY OF THE INVENTION

One aspect of the disclosure is a flexible circuit electrode array withmore than one layer of metal traces comprising: a polymer base layer;more than one layer of metal traces, separated by polymer layers,deposited on said polymer base layer, including electrodes suitable tostimulate neural tissue; and a polymer top layer deposited on saidpolymer base layer and said metal traces.

The novel features of the invention are set forth with particularity inthe appended claims. The invention will be best understood from thefollowing description when read in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the implanted portion of the preferredretinal prosthesis.

FIG. 2 is a side view of the implanted portion of the preferred retinalprosthesis showing the fan tail in more detail.

FIG. 3A-3 E depict molds for forming the flexible circuit array in acurve.

FIG. 4 depicts an alternate view of the invention with ribs to helpmaintain curvature and prevent retinal damage.

FIG. 5 depicts an alternate view of the invention with ribs to helpmaintain curvature and prevent retinal damage fold of the flexiblecircuit cable and a fold A between the circuit electrode array and theflexible circuit cable.

FIG. 6 depicts a cross-sectional view of the prosthesis shown insight ofthe eye with an angle in the fold of the flexible circuit cable and afold between the circuit electrode array and the flexible circuit cable.

FIG. 7 depicts the implanted portion including a twist in the array toreduce the width of a sclerotomy and a sleeve to promote sealing of thesclerotomy.

FIG. 8 depicts the flexible circuit array before it is folded andattached to the implanted portion.

FIG. 9 depicts the flexible circuit array folded.

FIG. 10 depicts a flexible circuit array with a protective skirt.

FIG. 11 depicts a flexible circuit array with a protective skirt bondedto the back side of the flexible circuit array.

FIG. 12 depicts a flexible circuit array with a protective skirt bondedto the front side of the flexible circuit array.

FIG. 13 depicts a flexible circuit array with a protective skirt bondedto the back side of the flexible circuit array and molded around theedges of the flexible circuit array.

FIG. 14 depicts a flexible circuit array with a protective skirt bondedto the back side of the flexible circuit array and molded around theedges of the flexible circuit array and flush with the front side of thearray.

FIG. 15 is an enlarged view of a single electrode within the flexiblecircuit electrode array.

FIG. 16 depicts the flexible circuit array before it is folded andattached to the implanted portion containing an additional fold betweenthe flexible electrode array and the flexible cable.

FIG. 17 depicts the flexible circuit array of FIG. 16 folded containingan additional fold between the flexible electrode array and the flexiblecable.

FIG. 18 depicts a flexible circuit array of FIG. 17 with a protectiveskirt and containing an additional fold between the flexible electrodearray and the flexible cable.

FIG. 19 depicts a top view of a flexible circuit array and flexiblecircuit cable showing an additional horizontal angel between theflexible electrode array and the flexible cable.

FIG. 20 depicts another variation without the horizontal angel betweenthe flexible electrode array and the flexible cable but with anorientation of the electrodes in the flexible electrode array as shownfor the variation in FIG. 19.

FIG. 21 depicts a top view of a flexible circuit array and flexiblecircuit cable wherein the array contains a slit along the length axis.

FIG. 22 depicts a top view of a flexible circuit array and flexiblecircuit cable wherein the array contains a slit along the length axiswith a two attachment points.

FIG. 23 depicts a flexible circuit array with a protective skirt bondedto the back side of the flexible circuit array with a progressivelydecreasing radius.

FIG. 23 a depicts a variation of a flexible circuit array with aprotective skirt bonded to the back side of the flexible circuit arraywith a progressively decreasing radius.

FIG. 24 depicts a flexible circuit array with a protective skirt bondedto the front side of the flexible circuit array with a progressivelydecreasing radius.

FIG. 25 depicts a flexible circuit array with a protective skirt bondedto the back side of the flexible circuit array and molded around theedges of the flexible circuit array with a progressively decreasingradius.

FIG. 26 depicts a flexible circuit array with a protective skirt bondedto the back side of the flexible circuit array and molded around theedges of the flexible circuit array and flush with the front side of thearray with a progressively decreasing radius.

FIG. 27 depicts a side view of the flexible circuit array with a skirtcontaining a grooved and rippled pad instead a suture tab.

FIG. 28 depicts a side view of the enlarged portion of the skirt shownin FIG. 27 containing a grooved and rippled pad and a mattress suture.

FIG. 29 depicts a flexible circuit array with a protective skirt bondedto the front side of the flexible circuit array with individualelectrode windows.

FIG. 30 depicts a flexible circuit array with a protective skirt bondedto the back side of the flexible circuit array and molded around theedges of the flexible circuit array with individual electrode windows.

FIGS. 31-36 show several surfaces to be applied on top of the cable.

FIG. 37 depicts the top view of the flexible circuit array beingenveloped within an insulating material.

FIG. 38 depicts a cross-sectional view of the flexible circuit arraybeing enveloped within an insulating material.

FIG. 39 depicts a cross-sectional view of the flexible circuit arraybeing enveloped within an insulating material with open electrodes andthe material between the electrodes.

FIG. 40 depicts a cross-sectional view of the flexible circuit arraybeing enveloped within an insulating material with open electrodes.

FIG. 41 depicts a cross-sectional view of the flexible circuit arraybeing enveloped within an insulating material with electrodes on thesurface of the material.

FIG. 42 depicts a cross-sectional view of the flexible circuit arraybeing enveloped within an insulating material with electrodes on thesurface of the material insight the eye with an angle in the fold of theflexible circuit cable and a fold between the circuit electrode arrayand the flexible circuit cable.

FIG. 43 depicts a side view of the enlarged portion of the flexiblecircuit array being enveloped within an insulating material withelectrodes on the surface of the material insight the eye.

FIG. 44 shows of front view of a cochlear electrode array according tothe present invention.

FIG. 45 shows a side view of a cochlear electrode array according to thepresent invention.

FIG. 46 shows a cochlear electrode array according to the presentinvention as implanted in the cochlea.

FIG. 47 to FIG. 67 depicts the sequence of a new process for producing aflexible circuit electrode array.

FIG. 47 depicts a cross-sectional view of substrate, comprising glass orsilicon.

FIG. 48 depicts a cross-sectional view of the substrate and a layer ofpolymer deposited on the substrate.

FIG. 49 depicts a cross-sectional view of the substrate with photoresistdeposited on the polymer.

FIG. 50 depicts a cross-sectional view of the layer structure andphotoresist after being exposed and developed.

FIG. 51 depicts a cross-sectional view of the layer structure afterpolymer etching.

FIG. 52 depicts a cross-sectional view of the layer structure afterstripping the photoresist.

FIG. 53 depicts a cross-sectional view of the layer structure afterdepositing thin film metals.

FIG. 54 depicts a cross-sectional view of the layer structure afterdepositing a photoresist layer on the thin film.

FIG. 55 depicts a cross-sectional view of the layer structure andphotoresist after being exposed and developed.

FIG. 56 depicts a cross-sectional view of the layer structure afteretching the thin film metal layer.

FIG. 57 depicts a cross-sectional view of the layer structure afterstripping the photoresist.

FIG. 58 depicts a cross-sectional view of the layer structure afterapplying a top polymer layer.

FIG. 59 depicts a cross-sectional view of the layer structure afterapplying a photoresist layer on the top polymer layer.

FIG. 60 depicts a cross-sectional view of the layer structure andphotoresist after being exposed and developed.

FIG. 61 depicts a cross-sectional view of the layer structure afteretching the top polymer layer.

FIG. 62 depicts a cross-sectional view of the layer structure afterstripping the photoresist.

FIG. 63 depicts a cross-sectional view of the layer structure afterreleasing the structure from the substrate.

FIG. 64 depicts a cross-sectional view of the layer structure turnedupside down and applied on a new substrate.

FIG. 65 depicts a cross-sectional view of the layer structure afteretching down the polymer layer to the metal layer.

FIG. 66 depicts a cross-sectional view of the layer structure withdeeper etching of the polymer to obtain protruding contacts

FIG. 67 depicts a cross-sectional view of the layer structure afterreleasing the structure from the substrate.

FIG. 68 depicts a top view of a part of the flexible electrode array.

FIG. 69 depicts a cross-sectional view of the layer structure withdeeper etching of the polymer to obtain protruding contacts.

FIG. 70 depicts a top view of a cluster of column shaped electrodes.

FIG. 71 depicts a top view of a star shaped electrode having a highratio of parameter length to surface area.

FIG. 72 depicts a top view of a cluster of a column shaped electrodehaving a high ratio of parameter length to surface area.

FIG. 73 depicts a top view of an annular shaped electrode.

FIG. 74 depicts a cross-sectional view of a multilayer structure.

FIG. 75 depicts a cross-sectional view of a multilayer structure withinter layer vias.

FIG. 76 depicts a cross-sectional view of interlayer vias used to bridgetraces.

FIG. 76A depicts a top view of interlayer vias used to bridge traces.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is of the best mode presently contemplated forcarrying out the invention. This description is not to be taken in alimiting sense, but is made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe determined with reference to the claims.

Polymer materials are useful as electrode array bodies for neuralstimulation. They are particularly useful for retinal stimulation tocreate artificial vision, cochlear stimulation to create artificialhearing, or cortical stimulation for many purposes. Regardless of whichpolymer is used, the basic construction method is the same. A layer ofpolymer is laid down, commonly by some form of chemical vapordeposition, spinning, meniscus coating or casting. A layer of metal,preferably platinum, is applied to the polymer and patterned to createelectrodes and leads for those electrodes. Patterning is commonly doneby photolithographic methods. A polymer second layer 75 is applied overthe metal layer and patterned to leave openings for the electrodes, oropenings are created later by means such as laser ablation. Hence thearray and its supply cable are formed of a single body. Alternatively,multiple alternating layers of metal and polymer may be applied toobtain more metal traces within a given width.

The pressure applied against the retina, or other neural tissue, by anelectrode array is critical. Too little pressure causes increasedelectrical resistance between the array and retina, along with electricfield dispersion. Too much pressure may block blood flow causing retinalischemia and hemorrhage. Pressure on the neural retina may also blockaxonal flow or cause neuronal atrophy leading to optic atrophy. Commonflexible circuit fabrication techniques such as photolithographygenerally require that a flexible circuit electrode array be made flat.Since the retina is spherical, a flat array will necessarily apply morepressure near its edges, than at its center. Further, the edges of aflexible circuit polymer array may be quite sharp and cut the delicateretinal tissue. With most polymers, it is possible to curve them whenheated in a mold. By applying the right amount of heat to a completedarray, a curve can be induced that matches the curve of the retina. Witha thermoplastic polymer such as liquid crystal polymer, it may befurther advantageous to repeatedly heat the flexible circuit in multiplemolds, each with a decreasing radius. Further, it is advantageous to addmaterial along the edges of a flexible circuit array. Particularly, itis advantageous to add material that is more compliant than the polymerused for the flexible circuit array.

It is further advantageous to provide a fold or twist in the flexiblecircuit array at the point where it passes through the sclera.Additional material may be added inside and outside the fold to promotea good seal with the scleral tissue.

FIG. 1 shows a perspective view of the implanted portion of thepreferred retinal prosthesis. A flexible circuit 1 includes a flexiblecircuit electrode array 10 which is mounted by a retinal tack (notshown) or similar means to the epiretinal surface. The flexible circuitelectrode array 10 is electrically coupled by a flexible circuit cable12, which pierces the sclera and is electrically coupled to anelectronics package 14, external to the sclera.

The electronics package 14 is electrically coupled to a secondaryinductive coil 16. Preferably the secondary inductive coil 16 is madefrom wound wire. Alternatively, the secondary inductive coil 16 may bemade from a flexible circuit polymer sandwich with wire traces depositedbetween layers of flexible circuit polymer. The electronics package 14and secondary inductive coil 16 are held together by a molded body 18.The molded body 18 may also include suture tabs 20. The molded body 18narrows to form a strap 22 which surrounds the sclera and holds themolded body 18, secondary inductive coil 16, and electronics package 14in place. The molded body 18, suture tabs 20 and strap 22 are preferablyan integrated unit made of silicone elastomer. Silicone elastomer can beformed in a pre-curved shape to match the curvature of a typical sclera.However, silicone remains flexible enough to accommodate implantationand to adapt to variations in the curvature of an individual sclera. Thesecondary inductive coil 16 and molded body 18 are preferably ovalshaped. A strap 22 can better support an oval shaped coil.

It should be noted that the entire implant is attached to and supportedby the sclera. An eye moves constantly. The eye moves to scan a sceneand also has a jitter motion to improve acuity. Even though such motionis useless in the blind, it often continues long after a person has losttheir sight. By placing the device under the rectus muscles with theelectronics package in an area of fatty tissue between the rectusmuscles, eye motion does not cause any flexing which might fatigue, andeventually damage, the device.

FIG. 2 shows a side view of the implanted portion of the retinalprosthesis, in particular, emphasizing the fan tail 24. When implantingthe retinal prosthesis, it is necessary to pass the strap 22 under theeye muscles to surround the sclera. The secondary inductive coil 16 andmolded body 18 must also follow the strap 22 under the lateral rectusmuscle on the side of the sclera. The implanted portion of the retinalprosthesis is very delicate. It is easy to tear the molded body 18 orbreak wires in the secondary inductive coil 16. In order to allow themolded body 18 to slide smoothly under the lateral rectus muscle, themolded body 18 is shaped in the form of a fan tail 24 on the endopposite the electronics package 14.

The flexible circuit 1 is a made by the following process. First, alayer of polymer (such as polyimide, fluoro-polymers, silicone or otherpolymers) is applied to a support substrate (not part of the array) suchas glass. Layers may be applied by spinning, meniscus coating, casting,sputtering or other physical or chemical vapor deposition, or similarprocess. Subsequently, a metal layer is applied to the polymer. Themetal is patterned by photolithographic process. Preferably, aphoto-resist is applied and patterned by photolithography followed by awet etch of the unprotected metal. Alternatively, the metal can bepatterned by lift-off technique, laser ablation or direct writetechniques.

It is advantageous to make this metal thicker at the electrode and bondpad to improve electrical continuity. This can be accomplished throughany of the above methods or electroplating. Then, the top layer ofpolymer is applied over the metal. Openings in the top layer forelectrical contact to the electronics package 14 and the electrodes maybe accomplished by laser ablation or reactive ion etching (RIE) orphotolithograph and wet etch. Making the electrode openings in the toplayer smaller than the electrodes promotes adhesion by avoidingdelaminating around the electrode edges.

The pressure applied against the retina by the flexible circuitelectrode array is critical. Too little pressure causes increasedelectrical resistance between the array and retina. It should be notedthat while the present invention is described in terms of application tothe retina, the techniques described are equally applicable to manyforms of neural stimulation. Application to the retina requires a convexspherical curve. Application to the cochlea requires a constant curve inone dimension and a spiral curve in the other. Application to thecerebral cortex requires a concave spherical curve. Cortical stimulationis useful for artificial vision or hearing, touch and motor control forlimb prostheses, deep brain stimulation for Parkinson's disease andmultiple sclerosis, and many other applications.

Common flexible circuit fabrication techniques such as photolithographygenerally require that a flexible circuit electrode array be made flat.Since the retina is spherical, a flat array will necessarily apply morepressure near its edges, than at its center. With most polymers, it ispossible to curve them when heated in a mold. By applying the rightamount of heat to a completed array, a curve can be induced that matchesthe curve of the retina. To minimize warping, it is often advantageousto repeatedly heat the flexible circuit in multiple molds, each with adecreasing radius. FIG. 3 illustrates a series of molds according to thepreferred embodiment. Since the flexible circuit will maintain aconstant length, the curvature must be slowly increased along thatlength. As the curvature 30 decreases in successive molds (FIGS. 3A-3E)the straight line length between ends 32 and 34, must decrease to keepthe length along the curvature 30 constant, where mold 3E approximatesthe curvature of the retina or other desired neural tissue. The moldsprovide a further opening 36 for the flexible circuit cable 12 of thearray to exit the mold without excessive curvature.

It should be noted that suitable polymers include thermoplasticmaterials and thermoset materials. While a thermoplastic material willprovide some stretch when heated a thermoset material will not. Thesuccessive molds are, therefore, advantageous only with a thermoplasticmaterial. A thermoset material works as well in a single mold as it willwith successive smaller molds. It should be noted that, particularlywith a thermoset material, excessive curvature in three dimensions willcause the polymer material to wrinkle at the edges. This can causedamage to both the array and the retina. Hence, the amount of curvatureis a compromise between the desired curvature, array surface area, andthe properties of the material.

Referring to FIG. 4, the edges of the polymer layers are often sharp.There is a risk that the sharp edges of a flexible circuit will cut intodelicate retinal tissue. It is advantageous to add a soft material, suchas silicone, to the edges of a flexible circuit electrode array to roundthe edges and protect the retina. Silicone around the entire edge maymake the flexible circuit less flexible. So, it is advantageous toprovide silicone bumpers or ribs to hold the edge of the flexiblecircuit electrode array away from the retinal tissue. Curvature 40 fitsagainst the retina. The leading edge 44 is most likely to cause damageand is therefore fit with molded silicone bumper. Also, edge 46, wherethe array lifts off the retina can cause damage and should be fit with abumper. Any space along the side edges of curvature 40 may cause damageand may be fit with bumpers as well. It is also possible for theflexible circuit cable 12 of the electrode array to contact the retina.It is, therefore, advantageous to add periodic bumpers along theflexible circuit cable 12.

It is also advantageous to create a reverse curve or service loop in theflexible circuit cable 12 of the flexible circuit electrode array togently lift the flexible circuit cable 12 off the retina and curve itaway from the retina, before it pierces the sclera at a sclerotomy. Itis not necessary to heat curve the service loop as described above, theflexible circuit electrode array can simply be bent or creased uponimplantation. This service loop reduces the likelihood of any stressexerted extraocularly from being transmitted to the electrode region andretina. It also provides for accommodation of a range of eye sizes.

With existing technology, it is necessary to place the implanted controlelectronics outside of the sclera, while a retinal flexible circuitelectrode array must be inside the sclera in order to contact theretina. The sclera is cut through at the pars plana, forming asclerotomy, and the flexible circuit passed through the sclerotomy. Aflexible circuit is thin but wide. The more electrode wires, the widerthe flexible circuit must be. It may be difficult to seal a sclerotomyover a flexible circuit wide enough to support enough wires for a highresolution array. A narrow sclerotomy is preferable.

FIG. 5 depicts a further embodiment of the part of the prosthesis shownin FIG. 4 with a fold A between the circuit electrode array 10 and theflexible circuit cable 12. The angle in the fold A also called ankle hasan angle of 1°-180°, preferably 80°-120°. The fold A is advantageoussince it reduces tension and enables an effective attachment of theflexible electrode circuit array 10 to the retina.

FIG. 6 depicts a side view of the prosthesis inside an eye with an angleK of the flexible circuit cable 12 and a fold A between the circuitelectrode array 10 and the flexible circuit cable 12. The angle K isabout 45°-180° and preferably 80°-100°. The fold K also called knee isadvantageous because it decreases pressure which would be applied by theflexible circuit cable 10.

FIG. 7 shows the implanted portion of the retinal prosthesis includingthe additional feature of a gentle twist or fold 48 in the flexiblecircuit cable 12, where the flexible circuit cable 12 passes through thesclera (sclerotomy). The twist may be a simple sharp twist, or fold 48;or it may be a longer twist, forming a tube. While the tube is rounder,it reduces the flexibility of the flexible circuit. A simple fold 48reduces the width of the flexible circuit with only minimal impact onflexibility.

Further, silicone or other pliable substance may be used to fill thecenter of the tube or fold 48 formed by the twisted flexible circuitcable 12. Further it is advantageous to provide a sleeve or coating 50that promotes healing of the sclerotomy. Polymers such as polyimide,which may be used to form the flexible circuit cable 12 and flexiblecircuit electrode array 10, are generally very smooth and do not promotea good bond between the flexible circuit cable 12 and scleral tissue. Asleeve or coating of polyester, collagen, silicone, Gore-tex or similarmaterial would bond with scleral tissue and promote healing. Inparticular, a porous material will allow scleral tissue to grow into thepores promoting a good bond.

Alternatively, the flexible circuit electrode array 10 may be insertedthrough the sclera, behind the retina and placed between the retina andchoroid to stimulate the retina subretinally. In this case, it isadvantageous to provide a widened portion, or stop, of the flexiblecircuit cable 12 to limit how far the flexible circuit electrode arrayis inserted and to limit the transmission of stress through the sclera.The stop may be widening of the flexible circuit 1 or it may be addedmaterial such as a bumper or sleeve.

Human vision provides a field of view that is wider than it is high.This is partially due to fact that we have two eyes, but even a singleeye provides a field of view that is approximately 90° high and 140° to160° degrees wide. It is therefore, advantageous to provide a flexiblecircuit electrode array 10 that is wider than it is tall. This isequally applicable to a cortical visual array. In which case, the widerdimension is not horizontal on the visual cortex, but corresponds tohorizontal in the visual scene.

FIG. 8 shows the flexible circuit electrode array prior to folding andattaching the array to the electronics package 14. At one end of theflexible circuit cable 12 is an interconnection pad 52 for connection tothe electronics package 14. At the other end of the flexible circuitcable 12 is the flexible circuit electrode array 10. Further, anattachment point 54 is provided near the flexible circuit electrodearray 10. A retina tack (not shown) is placed through the attachmentpoint 54 to hold the flexible circuit electrode array 10 to the retina.A stress relief 55 is provided surrounding the attachment point 54. Thestress relief 55 may be made of a softer polymer than the flexiblecircuit, or it may include cutouts or thinning of the polymer to reducethe stress transmitted from the retina tack to the flexible circuitelectrode array 10. The flexible circuit cable 12 is formed in a dog legpattern so than when it is folded at fold 48 it effectively forms astraight flexible circuit cable 12 with a narrower portion at the fold48 for passing through the sclerotomy.

FIG. 9 shows the flexible circuit electrode array after the flexiblecircuit cable 12 is folded at the fold 48 to form a narrowed section.The flexible circuit cable 12 may include a twist or tube shape as well.With a retinal prosthesis as shown in FIG. 1, the bond pad 52 forconnection to the electronics package 14 and the flexible circuitelectrode array 10 are on opposite side of the flexible circuit. Thisrequires patterning, in some manner, both the base polymer layer and thetop polymer layer. By folding the flexible circuit cable 12 of theflexible circuit electrode array 10, the openings for the bond pad 52and the electrodes are on the top polymer layer and only the top polymerlayer needs to be patterned.

Also, since the narrowed portion of the flexible circuit cable 12pierces the sclera, shoulders formed by opposite ends of the narrowedportion help prevent the flexible circuit cable 12 from moving throughthe sclera. It may be further advantageous to add ribs or bumps ofsilicone or similar material to the shoulders to further prevent theflexible circuit cable 12 from moving through the sclera.

Further it is advantageous to provide a suture tab 56 in the flexiblecircuit body near the electronics package to prevent any movement in theelectronics package from being transmitted to the flexible circuitelectrode array 10. Alternatively, a segment of the flexible circuitcable 12 can be reinforced to permit it to be secured directly with asuture.

An alternative to the bumpers described in FIG. 4, is a skirt ofsilicone or other pliable material as shown in FIGS. 10, 11, 12, and 13.A skirt 60 covers the flexible circuit electrode array 10, and extendsbeyond its edges. It is further advantageous to include wings 62adjacent to the attachment point 54 to spread any stress of attachmentover a larger area of the retina. There are several ways of forming andbonding the skirt 60. The skirt 60 may be directly bonded throughsurface activation or indirectly bonded using an adhesive.

Alternatively, a flexible circuit electrode array 10 may be layeredusing different polymers for each layer. Using too soft of a polymer mayallow too much stretch and break the metal traces. Too hard of a polymermay cause damage to delicate neural tissue. Hence a relatively hardpolymer, such a polyimide may be used for the bottom layer and arelatively softer polymer such a silicone may be used for the top layerincluding an integral skirt to protect delicate neural tissue.

The simplest solution is to bond the skirt 60 to the back side (awayfrom the retina) of the flexible circuit electrode array 10 as shown inFIG. 11. While this is the simplest mechanical solution, sharp edges ofthe flexible circuit electrode array 10 may contact the delicate retinatissue. Bonding the skirt to the front side (toward the retina) of theflexible circuit electrode array 10, as shown in FIG. 12, will protectthe retina from sharp edges of the flexible circuit electrode array 10.However, a window 62 must be cut in the skirt 60 around the electrodes.Further, it is more difficult to reliably bond the skirt 60 to theflexible circuit electrode array 10 with such a small contact area. Thismethod also creates a space between the electrodes and the retina whichwill reduce efficiency and broaden the electrical field distribution ofeach electrode. Broadening the electric field distribution will limitthe possible resolution of the flexible circuit electrode array 10.

FIG. 13 shows another structure where the skirt 60 is bonded to the backside of the flexible circuit electrode array 10, but curves around anysharp edges of the flexible circuit electrode array 10 to protect theretina. This gives a strong bond and protects the flexible circuitelectrode array 10 edges. Because it is bonded to the back side andmolded around the edges, rather than bonded to the front side, of theflexible circuit electrode array 10, the portion extending beyond thefront side of the flexible circuit electrode array 10 can be muchsmaller. This limits any additional spacing between the electrodes andthe retinal tissue.

FIG. 14 shows a flexible circuit electrode array 10 similar to FIG. 13,with the skirt 60, flush with the front side of the flexible circuitelectrode array 10 rather than extending beyond the front side. Whilethis is more difficult to manufacture, it does not lift the electrodesoff the retinal surface as with the array in FIG. 10. It should be notedthat FIGS. 11, 13, and 14 show skirt 60 material along the back of theflexible circuit electrode array 10 that is not necessary other than forbonding purposes. If there is sufficient bond with the flexible circuitelectrode array 10, it may advantageous to thin or remove portions ofthe skirt 60 material for weight reduction.

Referring to FIG. 15, the flexible circuit electrode array 10 ismanufactured in layers. A base layer of polymer 70 is laid down,commonly by some form of chemical vapor deposition, spinning, meniscuscoating or casting. A layer of metal 72 (preferably platinum) is appliedto the polymer base layer 70 and patterned to create electrodes 74 andtraces for those electrodes. Patterning is commonly done byphotolithographic methods. The electrodes 74 may be built up byelectroplating or similar method to increase the surface area of theelectrode 74 and to allow for some reduction in the electrodes 74 overtime. Similar plating may also be applied to the bond pads 52 (FIG.8-10). A top polymer layer 76 is applied over the metal layer 72 andpatterned to leave openings for the electrodes 74, or openings arecreated later by means such as laser ablation. It is advantageous toallow an overlap of the top polymer layer 76 over the electrodes 74 topromote better adhesion between the layers, and to avoid increasedelectrode reduction along their edges. The overlapping top layerpromotes adhesion by forming a clamp to hold the metal electrode betweenthe two polymer layers. Alternatively, multiple alternating layers ofmetal and polymer may be applied to obtain more metal traces within agiven width.

FIG. 16 depicts the flexible circuit array 12 before it is folded andattached to the implanted portion containing an additional fold Abetween the flexible electrode array 12 and the flexible cable 10. Theangle in the fold A also called ankle has an angle of 1°-180°,preferably 80°-120°. The ankle is advantageous in the process ofinserting the prostheses in the eye and attaching it to the retina.

FIG. 17 depicts the flexible circuit array 12 FIG. 16 folded containingan additional fold A between the flexible electrode array 12 and theflexible cable 10. The flexible circuit array as shown in FIGS. 8 and 16differ by the fold A from each other.

FIG. 18 depicts a flexible circuit array of FIG. 17 with a protectiveskirt 60 and containing an additional fold A between the flexibleelectrode array and the flexible cable. The flexible circuit array asshown in FIGS. 10 and 18 differ by the fold A from each other.

FIG. 19 depicts a top view of a flexible circuit electrode array andflexible circuit cable showing the additional horizontal angel H betweenthe flexible circuit electrode array 12 and the flexible circuit cable10. The angle H is from about 1° to about 90° and preferably from about30° to about 60°.

FIG. 20 depicts another variation without the horizontal angel H betweenthe flexible circuit electrode array 12 and the flexible circuit cable10 but with an orientation of the electrodes in the flexible circuitelectrode array 12 as shown in FIG. 19 for a flexible electrode array12. The grid of electrodes 13 has the angle H with the flexible cablewhich can be the same as the angel H in the flexible electrode array 12of FIG. 19.

Both variation shown in FIGS. 19 and 20 have the advantage that theelectrodes are oriented horizontally if they are inserted into the eye.Further, both variations as shown in FIGS. 19 and 20 can alsoadditionally contain a fold K.

FIG. 21 depicts a top view of a flexible circuit array and flexiblecircuit cable as shown in FIGS. 10 and 18 wherein the array contains aslit along the length axis.

FIG. 22 depicts a skirt of silicone or other pliable material as shownin FIGS. 10 to 14. A skirt 60 covers the flexible circuit electrodearray 10, and extends beyond its edges. In this embodiment of thepresent invention the flexible circuit electrode array contains a slit80 along the lengths axis. Further, according to this embodiment theskirt of silicone or other pliable material contains preferably at leasttwo attachment points 81 and stress reliefs 82 are provided surroundingthe attachment points 81. The attachment points 81 are locatedpreferably on the skirt 60 outside the flexible circuit electrode 10 andare positioned apart as far as possible from each other. The two tacks81 are far enough apart not to cause tenting, therefore fibrosis betweenthe two tacks which cause a traction detachment of the retina.Furthermore, the polyimide is completely between the two tacks, whichalso reduce the possibility of tenting. Also, this orientation of tackskeeps the tacks away from the axons, which arise from the ganglion cellswhich are tried to be activated. They are away from the raffe. The wingsact like external tabs or strain relieves. The multiple tacks preventrotation of the array.

The stress relief 82 may be made of a softer polymer than the flexiblecircuit, or it may include cutouts or thinning of the polymer to reducethe stress transmitted from the retina tack to the flexible circuitelectrode array 10.

FIG. 23 depicts a flexible circuit array 10 with a protective skirt 60bonded to the back side of the flexible circuit array 10 with aprogressively decreasing radius.

FIG. 23 a depicts a flexible circuit array 10 with a protective skirt 60bonded to the back side of the flexible circuit array 10 with aprogressively decreasing radius. This variation shows an angle x graterthan 90°. This angle is due to laser cutting. The laser cuts the polymerwith an angle x. This leaves a sharp edge y. To avoid that the sharpedge come into contact with the retina the polyimide layer is turnedaround after the laser cutting and attached up sight down to the skirt.

FIG. 24 depicts a flexible circuit array 10 with a protective skirt 60bonded to the front side of the flexible circuit array 10 with aprogressively decreasing radius.

FIG. 25 depicts a flexible circuit array 10 with a protective skirt 60bonded to the back side of the flexible circuit array 10 and moldedaround the edges of the flexible circuit array with a progressivelydecreasing radius.

FIG. 26 depicts a flexible circuit array 10 with a protective skirt 60bonded to the back side of the flexible circuit array 10 and moldedaround the edges of the flexible circuit array and flush with the frontside of the array with a progressively decreasing radius.

FIG. 27 depicts a side view of the array with a skirt 60 containing agrooved and rippled pad 56 a instead a suture tab 56. This pad 56 a hasthe advantage of capturing a mattress suture 57. A mattress suture 57has the advantage of holding the grove or rippled pad 56 a in two placesas shown in FIG. 28. Each suture 57 is fixed on the tissue on two places59. A mattress suture 57 on a grooved or rippled mattress 56 a thereforeprovides a better stability.

FIG. 29 depicts a flexible circuit array 10 with a protective skirt 60bonded to the front side of the flexible circuit array 10 withindividual electrode 13 windows and with material, preferably siliconbetween the electrodes 13.

FIG. 30 depicts a flexible circuit array with a protective skirt bondedto the back side of the flexible circuit array and molded around theedges of the flexible circuit array with individual electrode windowsand with material, preferably silicon between the electrodes 13.

FIGS. 31-36 show several surfaces to be applied on top of the cable. Thesurfaces are thin films containing a soft polymer, preferably silicone.FIG. 31 shows a flange 15: A flange 15 can be a solid film of materialcontaining silicone added to the surface of the polymer containingpolyimide. FIGS. 32-34 show a ladder 15 a: A ladder 15 a is a flangewith material removed from central portions in some shape 19. FIG. 35shows a skeleton structure 15 b. A skeleton 15 b is a flange withmaterial removed from perimeter portions in some shape 21. FIG. 36 showsa structure 15 c with beads 23 and bumpers 25. A bead 23 is materialadded to perimeter portions of the polymer cable in some shape withoutmaterial being added on the central area. A bumper 25 can be an extendedor continuous version of the beaded approach. Both approaches arehelpful in preventing any possible injury of the tissue by the polymer.

FIG. 37 depicts the top view of the flexible circuit array 10 beingenveloped within an insulating material 11. The electrode array 10comprises oval-shaped electrode array body 10, a plurality of electrodes13 made of a conductive material, such as platinum or one of its alloys,but that can be made of any conductive biocompatible material such asiridium, iridium oxide or titanium nitride. The electrode array 10 isenveloped within an insulating material 11 that is preferably silicone.“Oval-shaped” electrode array body means that the body may approximateeither a square or a rectangle shape, but where the corners are rounded.This shape of an electrode array is described in the U.S. PatentApplication No. 20020111658, entitled “Implantable retinal electrodearray configuration for minimal retinal damage and method of reducingretinal stress” and No. 20020188282, entitled “Implantable drug deliverydevice” to Rober J. Greenberg et al., the disclosures of both areincorporated herein by reference.

The material body 11 is made of a soft material that is compatible withthe electrode array body 10. In a preferred embodiment the body 11 madeof silicone having hardness of about 50 or less on the Shore A scale asmeasured with a durometer. In an alternate embodiment the hardness isabout 25 or less on the Shore A scale as measured with a durometer.

FIG. 38 depicts a cross-sectional view of the flexible circuit array 10being enveloped within an insulating material 11. It shows how the edgesof the material body 11 are lift off due to the contracted radius. Theelectrode array 10 preferably also contains a fold A between the cable12 and the electrode array 10. The angle of the fold A secures a reliefof the implanted material.

FIG. 39 depicts a cross-sectional view of the flexible circuit array 10being enveloped within an insulating material 11 with open electrodes 13and the material 11 between the electrodes 13. This embodiment also hasrelief between the body 10 and the retinal R.

FIG. 40 depicts a cross-sectional view of the flexible circuit array 10being enveloped within an insulating material 11 with open electrodes13. This is another embodiment wherein the electrodes 13 are notseparated by the material 11 but the material 11 is extended so that theelectrodes 13 are prevented of direct contact with the retina R.

FIG. 41 depicts a cross-sectional view of the flexible circuit array 10being enveloped within an insulating material 11 with electrodes 13 onthe surface of the material 11. This is a further embodiment with theelectrode 13 on the surface of the material 11, preferably silicone. Theembodiments shown in FIGS. 39, 40, and 41 show a preferred body 11containing silicone with the edges being lift off from the retina due tocontracted radius of the silicon body 11.

FIG. 42 depicts a cross-sectional view of the flexible circuit array 10being enveloped within an insulating material 11 with electrodes 13 onthe surface of the material 11 insight the eye with an angle K in thefold of the flexible circuit cable 12 and a fold A between the circuitelectrode array 10 and the flexible circuit cable 12. The material 11and electrode array body 10 are in intimate contact with retina R. Thesurface of electrode array body 10 in contact with retina R is a curvedsurface with a contracted radius compared to the spherical curvature ofretina R to minimize stress concentrations therein. Further, thedecreasing radius of spherical curvature of material 11 near its edgeforms edge relief that causes the edges of the body 11 to lift off thesurface of retina R eliminating stress concentrations. The edges of body11 are strongly lifted off due to the contracted radius of the body 11.The edge of body 11 has a rounded edge eliminating stress and cutting ofretina R.

FIG. 43 shows a part of the FIG. 42 enlarged showing the electrode array10 and the electrodes 13 enveloped by the polymer material, preferablysilicone 11 being attached to the retina R.

The electrode array 10 embedded in or enveloped by the polymer material,preferably silicone 11 can be preferably produced through the followingsteps. The soft polymer material which contains silicone is molded intothe designed shape and partially hardened. The electrode array 10 whichpreferably contains polyimide is introduced and positioned in thepartially hardened soft polymer containing silicone. Finally, the softpolymer 11 containing silicone is fully hardened in the designed shapeenveloping the electrode array 10. The polymer body 11 has a shape witha contracted radius compared with the retina R so that the edges of thebody 11 lift off from the retina R.

FIGS. 44-46 show application of the present invention to a cochlearprosthesis. FIG. 44 shows of front view of cochlear electrode array 110.The cochlear electrode array 110 tapers toward the top to fit in an eversmaller cochlea and because less width is required toward the top formetal traces. The electrodes 174 are arranged linearly along the lengthof the array 110. Further a skirt 160 of more compliant polymer, such assilicone surrounds the array 110. FIG. 45 is a side view of the cochlearelectrode array 110. The cochlear electrode array 110 includes a bottompolymer layer 170, metal traces 172 and a top polymer layer 176.Openings in the top polymer layer 176 define electrodes 174.

The cochlear electrode array 110 is made flat as shown if FIGS. 44 and13B. It is then thermoformed, as described above, into a spiral shape toapproximate the shape of the cochlea, as shown in FIG. 46. The cochlearelectrode array 110 is implanted with the bottom layer 170 formed towardthe outside of the curvature, and the top polymer layer 176 toward theinside of the curvature. This is opposite of the thermoforming processused for a retinal array. A cortical array would be thermoformed tocurve inward like a cochlear array.

FIG. 47 to FIG. 67 depict the sequence of a new process for producing aflexible circuit electrode array. The substrate S in that process can besilicon or glass. The polymer can be polyimide, thermoplastic polyimide,silicone, parylene, LCP polymers (Imidex), epoxy resin, PEEK (Victrex),TPE (Thermoplastic elastomer) or mixtures thereof. The metals can betitanium, platinum, palladium, iridium, gold, silver, niobium, titaniumnitride, iridium oxide, ruthenium, ruthenium oxide, rhodium or otherbiocompatible metals or metal alloys or metal layers.

FIG. 47 depicts a cross-sectional view of substrate, comprising glass orsilicon. FIG. 48 depicts a cross-sectional view of the substrate and alayer of polymer P deposited on the substrate. The polymer can bedeposited by spi- or dip coating or any other known method. FIG. 49depicts a cross-sectional view of the substrate with photoresist PRdeposited on the polymer. FIG. 50 depicts a cross-sectional view of thelayer structure and photoresist PR after being exposed and developed.The developing process includes irradiation of photoresist through atemplate mask and removing the developed parts of the photoresist. FIG.51 depicts a cross-sectional view of the layer structure after polymeretching. Polymer can be etched by reactive plasma, RIE, or laser IONmilling. FIG. 52 depicts a cross-sectional view of the layer structureafter stripping the photoresist PR. FIG. 53 depicts a cross-sectionalview of the layer structure after depositing thin film metals M. FIG. 54depicts a cross-sectional view of the layer M structure after depositinga photoresist layer PR on the thin film M. The metal thin film cancontain titanium, platinum, palladium, iridium, gold, silver, niobium,titanium nitride, iridium oxide or other biocompatible metals or metalalloys or metal layers. An adhesion layer containing for example Ti canbe applied on top and bottom of the thin metal layer M. FIG. 55 depictsa cross-sectional view of the layer structure and photoresist afterbeing exposed and developed (see for example arrow). FIG. 56 depicts across-sectional view of the layer structure after etching the thin filmmetal layer M by wet or dry etching (see for example arrow). FIG. 57depicts a cross-sectional view of the layer structure after strippingthe photoresist PR. FIG. 58 depicts a cross-sectional view of the layerstructure after applying a top polymer layer P2. FIG. 59 depicts across-sectional view of the layer structure after applying a photoresistlayer on the top polymer layer. FIG. 60 depicts a cross-sectional viewof the layer structure and photoresist PR after being exposed anddeveloped (see for example arrow). FIG. 61 depicts a cross-sectionalview of the layer structure after etching the top polymer layer P2 (seefor example arrow). FIG. 62 depicts a cross-sectional view of the layerstructure after stripping the photoresist. FIG. 63 depicts across-sectional view of the layer structure after releasing thestructure from the substrate. FIG. 64 depicts a cross-sectional view ofthe layer structure turned upside down and applied on a new substrateS2. FIG. 65 depicts a cross-sectional view of the layer structure afteretching down the polymer layer to the metal layer. FIG. 66 depicts across-sectional view of the layer structure with deeper etching of thepolymer to obtain protruding contacts. FIG. 67 depicts a cross-sectionalview of the layer structure after releasing the structure from thesubstrate.

FIG. 68 depicts a top view of a part of the flexible electrode array.

FIG. 69 depicts a cross-sectional view of the layer structure withdeeper etching of the polymer to obtain protruding contacts PC. Theprotruding contacts have a larger surface and that is an advantageversus flat surface.

FIGS. 70 to 73 show other electrode geometries as required to maximizecharge uniformity or surface area or contact with tissue, for example toimprove stimulus location. Circle shapes, star shapes, square shapes andrings are shown in the electrode array. Each of the shapes can containoverlapping edges and mesh grids. This presents a series of newelectrode geometries that control charge transfer characteristics by thestrategic use of edges and corners to concentrate current delivery.These designs are an improvement on conventional surface electrodedesigns which are typically circles. FIG. 70 depicts a top view of acluster of column shaped electrodes. FIG. 71 depicts a top view of astar shaped electrode having a high ratio of parameter length to surfacearea. FIG. 72 depicts a top view of a cluster of a column shapedelectrode having a high ratio of parameter length to surface area. FIG.73 depicts a top view of an annular shaped electrode.

FIGS. 74 to 76 show a cross-section of multilayer structure. The traces(metal) are in more than one layer, preferably two or three layers. Thisvariation allows a less broad conducting part of the electrode array.The advantage is that the conducting density is increased. Theconducting part can be made thinner by slightly increase of the depth.The increase of the depth has only minor influence on the flexibility ofthe conducting part. FIG. 76 shows filled via leading into a conductingpad. The current enters the electrode through via in the center and notat the edge. If the current is led to the electrode at the edge and theelectrode starts to dissolve at the edge to the insulating material itleads to a faster break up of the conductivity. The advantage of thepresent multilayer is that the conductivity stays stable because even ifthe electrode starts to dissolve at the edge to the insulating materialthe conductivity stays stable until the electrode dissolves completelytowards the center. Vias can be used to connect traces on differentmetal layers or to connect an electrode to a metal a trace.

FIG. 74 depicts a cross-sectional view of a multilayer structure. ITshows as an example two layers of traces T and T2. Trace T has a directcontact with an electrode. Trace T2 also has a direct contact to theelectrode E.

FIG. 75 depicts a cross-sectional view of a multilayer structure withinterlayer vias. Vias allow connections between multiple conductorlayer, here metal traces. FIG. 75 shows that the via passes the currentthrough the center of the electrode and not from the edge of theelectrode. This has a certain advantage because the edge of theelectrode has the tendency to dissolve faster.

FIG. 76 depicts a cross-sectional view of interlayer vias used to bridgetraces containing via in the trace. FIG. 76A depicts a top view ofinterlayer vias used to bridge traces.

This process could be easily adapted to a multi-metal layer electrodearray or similar metal and polymer structures that need to have metalcontacts or openings on both sides of the structure.

1. A method of making a flexible circuit electrode array comprising:depositing a polymer base layer; depositing a first metal layer on saidpolymer base layer; patterning said first metal to form first metaltraces; depositing a polymer interlayer on said polymer base layer andsaid metal traces; patterning said polymer interlayer to provide vias;depositing a second metal layer on said polymer interlayer; patterningsaid second metal layer to form second metal traces; depositing apolymer top layer on said polymer interlayer and said second metaltraces forming a flexible circuit; and embedding the flexible circuit inan curved body having a generally curved in the plane of a retina, thecurved body curved to conform to a spherical curvature of the retina. 2.The method according to claim 1, further comprising repeating the stepsof depositing metal layers patterning and depositing polymer interlayersto create additional trace layers.
 3. The method according to claim 1,wherein vias are created by MEMS process.
 4. The method according toclaim 1, wherein the steps of patterning polymer are etching by reactiveplasma.
 5. The method according to claim 1, wherein the steps ofpatterning polymer are etching by RIE.
 6. The method according to claim1, wherein the steps of patterning polymer are etching by Ion milling.7. The method according to claim 1, wherein the steps of patterningmetal layers is wet etching
 8. The method according to claim 1, whereinthe steps of patterning metal layers is dry etching.
 9. The methodaccording to claim 1, further comprising plating electrodes throughopenings in the polymer top layer.
 10. The method according to claim 9,wherein the step of plating is electroplating.
 11. The method accordingto claim 10, wherein the step of plating is electroplating platinumgrey.
 12. The method according to claim 9, wherein the step of platingis plating electrodes to protrude above the polymer top layer.
 13. Themethod according to claim 12, wherein the protruding electrodes areshaped as a circle, star, square, ring or other geometric arrangement.14. The method according to claim 1, further comprising creatingopenings in the polymer base layer to provide bond pads for attachingthe flexible circuit electrode array to an electronic device.
 15. Themethod according to claim 1, wherein the steps of depositing polymer aredepositing polyimide, thermoplastic polyimide, silicone, parylene, LCPpolymers, epoxy resin, PEEK, TPE, or mixtures thereof.
 16. The methodaccording to claim 1, wherein the steps of depositing metal aredepositing titanium, platinum, palladium, iridium, gold, silver,niobium, titanium nitride, iridium oxide, ruthenium, ruthenium oxide,rhodium or other biocompatible metals or metal alloys or metal layers.17. The method according to claim 1, wherein the steps of depositingmetal include depositing an adhesion layer and a conducting layer. 18.The method according to claim 17, wherein the adhesion layer containstitanium.
 19. The method according to claim 17, wherein the conductinglayer includes platinum.
 20. A method of making a flexible circuitelectrode array comprising: depositing a polymer base layer; depositinga first metal layer on said polymer base layer; patterning said firstmetal to form first metal traces; depositing a polymer interlayer onsaid polymer base layer and said metal traces; patterning said polymerinterlayer to provide vias; depositing a second metal layer on saidpolymer interlayer; patterning said second metal layer to form secondmetal traces; depositing a polymer top layer on said polymer interlayerand said second metal traces forming a flexible circuit; andthermoforming the flexible circuit electrode array in an approximatelyspherical shape curved to conform to a spherical curvature of a retina.